Immune and inflammatory responses occurring during dermal infestation by larvae of Lucilia cuprina can retard larval growth and development. This study examined the effect of 4 classes of humoral inflammatory mediators on larval growth in an in vitro assay. Mediators of plasma leakage (histamine, bradykinin, platelet-activating factor and serotonin), leucocyte chcmotactic agonists (activated complement, leukotriene B4 and interleukin-8), effector molecules of immune responses (interleukin-1beta tumour necrosis factor-alpha and interferon-gamma) and endotoxin all failed to inhibit larval growth. In contrast, immunoglobulins isolated from immune serum caused marked retardation of larval growth. The results suggest that humoral mediators of inflammatory and immune responses do not play a role in immune defence against Lucilia cuprina.